Vaso-occlusive devices or implants are used for a wide variety of reasons, including treatment of intra-vascular aneurysms. A common vaso-occlusive device takes the form of a soft, helically wound coil formed by winding a platinum (or platinum alloy) wire strand about a primary mandrel. The relative stiffness of the coil will depend, among other things, on its composition, the diameter of the wire strand, the diameter of the primary mandrel, and the pitch of the primary windings. The coil is then wrapped around a larger, secondary mandrel, and again heat treated to impart a secondary shape. For example, U.S. Pat. No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil that assumes a linear, helical primary shape when stretched for placement through the lumen of a delivery catheter, and a folded, convoluted secondary shape when released from the delivery catheter and deposited in the vasculature.
In order to deliver the vaso-occlusive coils to a desired site, e.g., an aneurysm, in the vasculature, it is well-known to first position a small profile, micro-catheter at the site using a steerable guidewire. Typically, the distal end of the micro-catheter is provided, either by the attending physician or by the manufacturer, with a selected pre-shaped bend, e.g., 45°, 90°, “J”, “S”, or other bending shape, depending on the particular anatomy of the patient, so that it will stay in a desired position for releasing one or more vaso-occlusive coil(s) into the aneurysm once the guidewire is withdrawn. A delivery or “pusher” wire is then passed through the micro-catheter, until a vaso-occlusive coil coupled to a distal end of the pusher wire is extended out of the distal end opening of the micro-catheter and into the aneurysm. The vaso-occlusive device is then released or “detached” from the end pusher wire, and the pusher wire is withdrawn back through the catheter. Depending on the particular needs of the patient, another occlusive device may then be pushed through the catheter and released at the same site.
One known way to release a vaso-occlusive coil from the end of the pusher wire is through the use of an electrolytically severable junction, which is a small exposed section or detachment zone located along a distal end portion of the pusher wire. The detachment zone is typically made of stainless steel and is located just proximal of the vaso-occlusive device. An electrolytically severable junction is susceptible to electrolysis and, thus, disintegrates when the pusher wire is electrically charged in the presence of an ionic solution, such as blood or other bodily fluids. Thus, once the detachment zone exits out of the catheter distal end and is exposed in the vessel blood pool of the patient, a current applied to the conductive pusher wire completes a circuit with an electrode attached to the patient's skin, or with a conductive needle inserted through the skin at a remote site, and the detachment zone rapidly disintegrates due to electrolysis.
When the coil is being delivered, an axial force on the pusher member must be generated to overcome frictional forces with the micro-catheter and resistance to coil deployment into the aneurysm. In order to prevent columnar buckling due to this axial force, the distal end of the pusher wire proximal of the detachment zone is typically provided with a relatively stiff polymer jacket, e.g., made of polytetrafluoroethylene (“PTFE”) and/or polyethyleneterephthalate (“PET”). While preventing axial compression, the stiff polymer jacket can change the distal bend shape of the delivery catheter and, thus, deflect the delivery catheter tip away from its desired position. For example, the stiff polymer jacket region may have a relatively long length (e.g., around 2 mm) which will inhibit the bending ability of the delivery device. The use of a stiff polymer jacket may also require the physician to relocate the catheter tip in the aneurysm during delivery of the occlusive device, or prior to placement of a further occlusive device, which undesirably extends the duration and risks of the procedure.
A relatively long pusher member junction can exacerbate the problem of conforming the vaso-occlusive coil and portion of the pusher member distal to the junction into the aneurysm. If these components do not fit in the aneurysm, the catheter can be pushed back and move out of position, which can leave a tail of the coil in the parent artery, or present difficulties in repositioning the micro-catheter for subsequent coils to be delivered. This is especially true in a tightly curved delivery catheter.
There thus is a need for an occlusive delivery system that retains good pushability while at the same time maintains good flexibility. For example, a delivery device is needed that includes a distal portion that is configured to resist axial compression while at the same time permitting radial bending.